$$U_{756}(x, y) = \frac{\left(1 - \sqrt{- 4 x \left(y + 1\right) + 1}\right)^{3}}{8 x^{3} \left(y + 1\right)^{2}}$$

$$T_{756}(n, m, k) = \frac{3 k {\binom{k + n}{m}} {\binom{3 k + 2 n}{n}}}{3 k + 2 n}$$